Re: Causation, Indexical facts &Self-sampling

From: Nick Bostrom <>
Date: Tue, 20 Apr 1999 21:10:24 +0000

> Date: Sat, 17 Apr 1999 17:03:16 -0400
Jacques M Mallah wrote:

> Suppose he'd have kids if on a certain measurement he
> saw spin up.
> If you draw many spins from a sample and they are found to be 50%
> up and 50% down, you can be reasonably sure that the quantum probability
> p to measure up is about 50%.

Yes, you are right that on the MWI, if Adam thinks there is a
substantial probability that the q.m. chance of a deer appearing is
substantial, then you wouldn't get the shift that the paper refers
to. And as you say, Adam could obtain evidence for the hypothesis
that the q.m chance is substantial from observing his situation. Of
course, this presupposes that we have managed to make sense of the
MWI so that it gives probabilities in agreement with q.m. even when
combined with the self-sampling assumption. This is not trivial. If
q.m. says that outcome A has probability 2/3 and ČA has probability
1/3, then there would have to be twice as many Adams observing A as
ČA. Moreover, the total number of Adams at any time should be roughly
constant (modulo such events as Adam dying). It wouldn't do, for
example, to just think of Adam as splitting everytime a measurement
is made, for then almost all Adams would live very near the
temporal end of the universe (if there is one). So it seems we would
have to postulate an infinite (and uncountable) number of worlds. But
then it is not easy to see how the SSA applies -- there would always
be an infinite number of worlds where Adam is observing A and an
equally large infinite number of worlds where he is observing ČA.

Nick Bostrom
Department of Philosophy, Logic and Scientific Method
London School of Economics
Received on Tue Apr 20 1999 - 13:12:28 PDT

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